An aircraft assembly generally includes a landing gear assembly, which is generally movable between a deployed condition, for take-off and landing, and a stowed condition for flight.
An actuator is provided for moving the landing gear assembly between the deployed condition and the stowed condition. This actuator is known in the art as a retraction actuator. A retraction actuator may have one end coupled to the airframe and another end coupled to the main strut such that extension and retraction of the actuator results in movement of the main strut between the deployed and stowed conditions.
It is common for a landing gear assembly to be arranged to move towards the deployed condition in the event of a failure of the retraction actuator. Initially, the main strut will move towards the deployed condition by way of gravity. One or more down-lock springs are generally provided to assist in moving the landing gear assembly to the deployed condition and locking it in that state by urging a preloading linkage to assume a locked condition in which the main strut is fully deployed and locked in that state by the lock link.
In a three point attachment landing gear assembly, also known as a single stay landing gear assembly, a brace or stay is generally provided to support the orientation of the main fitting when the landing gear is in the deployed condition. A stay generally includes a two bar linkage that can be unfolded to assume a generally aligned condition in which the stay is locked by a lock link to inhibit movement of the main strut.
In a four point attachment landing gear assembly, also known as a dual stay landing gear assembly, a pair of stays are coupled to a common main strut, with a forward stay extending in front of the main strut and an aft stay extending behind the main strut. The stays can be side stays provided on the same side of the main strut. In either case, a lock link is generally provided in conjunction with each stay to maintain the stay in the locked condition.
A lock link generally includes a two bar linkage between the stay centre joint and the main strut or airframe structure. The lock link in its locked position is kept over-centre against mechanical stops via down-lock springs. An actuator usually coupled between one of the lock link and stay linkages is used to overcome the spring force and pull the lock link out of lock to enable the stay to be folded, thereby permitting the main strut to be moved by the retraction actuator towards the stowed condition. In another example, the preloading linkage can be in the form of a toggle link.
When a landing gear is deployed for landing, aerodynamic loading results in elastic deformation of the assembly, which can change the nominal distance between the stay attachment points; this distance will be referred to herein as the ‘preloading distance’. This is particularly so for dual stay landing gears, where the attachment joints for the rearmost stay become closer to one another.
Down-lock springs are sized to overcome loads acting on an associated stay and/or lock link as a result of the change in landing gear geometry as it assumes the deployed condition. In order to reduce the amount of energy required from a down-lock spring, and therefore its size and mass, it is known for a stay to be manufactured to a length which corresponds to the preloading distance. These types of stay will be referred to as a ‘preloading linkage’. By providing a preloading linkage, the assembly is pre-loaded to help the down-lock spring to move the preloading linkage into a locked condition, enabling the down-lock spring to be smaller and/or lighter and in some cases also helping to ensure that both stays are locked.
In order to fit a preloading linkage into an aircraft assembly, it is necessary to set the assembly to change the distance between the first and second link attachment joints from the default distance to a distance which substantially corresponds to the preloading distance. The preloading linkage is often provided with adjustable fittings which can be used to adjust the link attachment joints in view of tolerances in the assembly.
In another example, the preloading linkage can be in the form of a shortening mechanism linkage, where the shock absorber or trailing arm requires to be shortened during retraction. The preloading linkage is used to ensure the correct stowage position and down-lock of the landing gear assembly.
In another example, the preloading linkage can be in the form of a rotating mechanism linkage, where the wheels require to be rotated during retraction. The preloading linkage is used to ensure the correct stowage position and down-lock of the landing gear assembly.
The present inventors have identified that preloading an aircraft assembly for attachment of a preloading linkage can be a difficult and/or a time consuming operation. Also, it can be challenging to force the assembly to accurately achieve the preloading distance.